Pipeline systems are extremely pervasive and found virtually in any area of the world. Their uses are varied and adapted to suit the particular system needs and geographic area served. However, in general, pipeline systems include extremely long often varied pipelines formed together with a plurality of pumps and valve networks to form a complex pipeline system. The liquids commonly transferred by such pipeline systems are often flammable and produce gases which are explosive in nature. Common examples of pipeline systems include those carrying oil or other petroleum products, industrial liquid systems, or chemical industrial processing systems. In all pipeline systems, a need arises from time to time to perform either maintenance or repair work or system alteration upon existing pipelines. In such case, it is necessary to cut into a pipeline system and produce open ends of the pipelines to perform the desired work. The presence within the system of the above-mentioned flammable liquids and explosive gases create a hazardous environment in and around any open pipeline. To minimize or reduce the danger associated with operations near and upon such open pipelines, practitioners in the art are usually required to temporarily plug or seal the open ends of the pipeline systems. The reliable maintenance of such temporary seals or plugs is made all the more difficult due to the tendency of such pipelines to develop gas pressures or vacuums within the confined system near the temporary plug or seal. In addition, because the pipeline systems are usually dynamic, ongoing processes including the interaction of other pipelines, temperature effects, and the volatile nature of the liquids within the system cause the existing pressures or vacuums to which the sealing temporary plug is subjected to vary. Thus, any temporary seal or plug secured to an open pipeline must be capable of simultaneously resisting both pressure increases and decreases as well as the creation of substantial vacuums within the system. Thus, improperly installed or improperly designed or unreliable sealing plugs may, in the presence of extreme gas pressure, be blown from the open pipe end creating extreme hazard and releasing explosive gases. On the other hand, during high vacuum, such plugs may be drawn into the system and carried substantial distances within the pipeline rendering them difficult to locate and retrieve.
In addition to the need for such temporary seal plugs to resist both vacuum and pressure, their structures must accommodate and interfere to a minimum with the ongoing work performed upon the pipeline open end. In many operations, the pipeline end must be precision cut to facilitate its reunion with the existing system using techniques such as precision welding or the like. Thus, in a typical pipeline repair or modification operation, an initial portion of the existing pipeline is cut and removed leaving to open end portions. A temporary plug is situated within the to-be-serviced pipeline end in a sealing attachment. A retainer or anchor of some sort must then be secured between the plug and a fixed object to prevent the vacuum drawing plug down the pipeline mentioned above. Thereafter, in a typical operation, a precision cut is made upon the pipe and the cut portion is removed leaving a precision edge. It is important that the pipeline plug be compatible with the cutting and removal of this additional piece.
The continuing need for pipeline operations safety has prompted practitioners in the art to provide various structures for temporary plugging of pipelines. U.S. Pat. No. 4,658,860 issued to Reaux sets forth a PRESSURE SET AND RETRIEVABLE VENTED ANCHOR-SEAL FOR PIPELINE SERVICE in which a temporary plug includes an anchor and seal which are simultaneously operable and actuated by remote pressure application to ensure securement of the temporary plug while work is undertaken. A pressure test plug and valve are coupled to the plug to determine pressure and release pressure prior to tool removal. Anchor means are retractably supported upon the plug and configured to engage the pipeline to resist movement of the plug within the pipeline.
U.S. Pat. No. 3,503,424 issued to Sawyer sets forth a PIPELINE PLUGGING PIG AND METHOD FOR TEMPORARILY PLUGGING PIPELINES in which an elongated generally cylindrical pipeline plug includes an inflatable resilient seal together with mechanical anchoring means which cooperate with a plurality of inwardly extending pins secured within the interior of the pipeline passage.
U.S. Pat. No. 3,495,626 issued to Nagel sets forth PIPELINE PLUGGING APPARATUS AND METHODS in which a temporary pipeline plug is movable through the pipeline under propulsion of the fluid product within the line. The plugging apparatus is operated by transmitting signals through the pipeline walls to provide stopping, sealing and bypass venting functions. A plurality of plugging and sealing systems are shown which cooperate with the transmission and reception of control signals to provide the movable plugging function.
U.S. Pat. No. 3,902,528 issued to Tartabini, et al. sets forth a PNEUMATIC PLUG FOR HYDRAULIC CONDUITS in which a tubular metal mandrel and longitudinally coextensive external elastomeric sleeve bonded thereto provide a low cost inflatable element which may be used to provide an air pressurized seal within a hydraulic pipeline.
U.S. Pat. No. 3,746,300 issued to Welker sets forth a FLOW REGULATOR for a pipeline or the like which includes a plug of resilient material. The plug is expanded and bulges on its outer surface to provide a sealing action within the interior passage of a pipeline. A plurality of ribs on the downstream portion of the expandable plugs are secured to an encircling rib and are operative to control and limit the shape of the expandable plug to maintain sealing action.
While the foregoing described prior art devices have provided some measure of operability in pipeline systems maintenance and repair activities, there remains a continuing need for evermore reliable and safe temporary pipeline plugs throughout the pipeline industries.